Multi-band filter module and method of fabricating the same

ABSTRACT

A multi-band filter module and a method of fabricating the same are provided. The multi-band filter module includes a piezoelectric substrate, a first filter provided on the piezoelectric substrate, and a second filter provided adjacent to the first filter on the piezoelectric substrate, and operating in a frequency band that is lower than that of the first filter.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a Divisional application of U.S. application Ser. No. 11/646,502 filed Dec. 28, 2006, which claims priority from Korean Patent Application No. 10-2006-0071079, filed Jul. 27, 2006, in the Korean Intellectual Property Office, the entire contents of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Apparatuses and methods consistent with the present invention relate to a filter module, and more particularly to a multi-band filter module available in various frequency bands and a method of fabricating the same.

2. Description of the Related Art

Recently, as telecommunication appliances represented by mobile phones are rapidly popularized, a demand for a thin and light filter for use in these appliances is also increased.

In particular, as the telecommunication appliances are miniaturized and complicated, there is a necessity for a small-sized terminal available in various frequency bands. In order to utilize various frequency bands, a multi-band filter is acutely needed to filter only required frequencies among signals received through one antenna. An existing method of implementing a multi-band filter by use of a ceramic filter has weak competitiveness in comparison with an FBAR (Film Bulk Acoustic Resonator) or a SAW (Surface Acoustic Wave) device in view of its size and property.

Up to now, the smallest device having a good frequency characteristic in the band of 2 GHz is the FBAR using the bulk acoustic characteristic, while the smallest device having a good performance in the band of 900 MHz is the SAW device using the surface acoustic characteristic.

The FBAR has the advantages of mass production and miniaturization. Also, the FBAR has a high quality factor that is a major property of a filter, and can be used in a micro frequency band, in particular, in the bands of a PCS (Personal Communication System) and a DCS (Digital Cordless System).

The FBAR is generally fabricated by sequentially depositing a lower electrode, a piezoelectric layer, and an upper electrode on a substrate. According to the operating principle of the BRAR device, an electric energy is applied to the electrodes to induce an electric field that is temporally varied in the piezoelectric layer, and then the electric field causes a bulk acoustic wave in the same direction as a vibration direction of a resonant part in the piezoelectric layer to generate resonance therein.

Both the FBAR and the SAW device utilize the RF characteristic by use of the acoustic resonance. However, the SAW device can obtain a good characteristic by use of a specific piezoelectric substrate only. In the case of the FBAR, although it is not limited to a substrate, a silicon substrate is generally used so as to be inexpensive, integrated and compatible with IC.

A common multi-band filter is generally fabricated by separately making the above filter devices and combining the same with chips and trimming circuits through additional package. The method of fabricating the multi-band filter by using a separate filter has the problems of a complicated construction, many defective factors such as a short circuit of a device, and an increased size thereof.

Accordingly, a need exists for a development of a multi-band filter module having a thin and simple construction and fabricated by a simple method.

SUMMARY OF THE INVENTION

An aspect of the present invention is to provide a multi-band filter module into which a FBAR and a SAW device are integrated, and a method of fabricating the same.

The foregoing and other objects and advantages are substantially realized by providing a multi-band filter module, according to embodiments of the present invention, which comprises a piezoelectric substrate, a first filter provided on the piezoelectric substrate, and a second filter provided adjacent to the first filter on the piezoelectric substrate, and operating in a frequency band lower than that of the first filter.

The first filter may comprise an FBAR (film Bulk Acoustic Resonator).

The FBAR may comprise an air gap provided on the piezoelectric substrate, a resonant part located on the air gap and having a first electrode, a piezoelectric film, and a second electrode which are sequentially deposited, and an electrode pad connected to the first and second electrodes.

The second filter may include a SAW (Surface Acoustic Wave) device, and a SAW electrode pad provided on an upper surface of the piezoelectric substrate.

In another aspect of the present invention, there is provided a method of fabricating a multi-band filter module, which comprises (a) forming an FBAR on a piezoelectric substrate, and (b) forming a SAW device on the piezoelectric substrate, in which the steps (a) and (b) are concurrently performed.

The step (a) may comprise (a1) forming a sacrificial layer to form an air gap to be recessed on a surface of the piezoelectric substrate, (a2) sequentially depositing a first electrode, a piezoelectric plate, and a second electrode on the piezoelectric substrate to form a resonant part, (a3) depositing an electrode pad to be connected to the first and second electrodes, and (a4) removing the sacrificial layer to form the air gap corresponding to the resonant part.

The step (b) may comprise (b1) patterning the SAW device on the piezoelectric substrate, and (b 2 ) forming a SAW pad to be connected to the SAW device.

The step (b1) may be performed at the same time when the first electrode is formed in the step (a 2 ).

The step (b 2 ) may be performed concurrent with the step (a 3 ).

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawing figures, wherein;

FIG. 1 is a cross-sectional view illustrating a multi-band filter module according to an embodiment of the present invention;

FIGS. 2A to 2E are cross-sectional views explaining a process of fabricating the multi-band filter module in FIGS. 1; and

FIG. 2F is a cross-sectional view illustrating a packaged state of the multi-band filter module in FIG. 1.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE PRESENT INVENTION

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawing figures.

In the following description, same drawing reference numerals are used for the same elements even in different drawings. The matters defined in the description such as a detailed construction and elements are nothing but the ones provided to assist in a comprehensive understanding of the invention. Thus, it is apparent that the present invention can be carried out without those defined matters. Also, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail.

FIG. 1 is a cross-sectional view illustrating a multi-band filter module according to an embodiment of the present invention.

Referring to FIG. 1, the multi-band filter module of the present invention is to filter each required frequency among the signal received by one antenna. More specifically, there is shown a filter module fabricated by simultaneously integrating SAW for a cellular band and FBAR for PCS on the same substrate.

Referring to FIG. 1, the multi-band filter module includes a piezoelectric substrate 10, and first and second filters formed on the piezoelectric substrate 10.

The piezoelectric substrate 10 can be made of a specific single crystal piezoelectric substance, for example, LiTaO₃ or LiNbO₃.

The first filter includes an FBAR 20. The FBAR 20 has an air gap 21 formed on the upper surface of the piezoelectric substrate 10, a resonant part 22 formed on the upper surface of the air gap 21, and a pair of electrode pads 23 and 24.

The air gap 21 is formed to have a specific depth extending downwardly from the upper surface of the piezoelectric substrate 10. The air gap 21 is formed under the resonant part 22. The air gap 21 can be created by forming a sacrificial layer to have a specific depth from the upper surface of the piezoelectric substrate 10 and then removing the same.

The resonant part 22 has a first electrode 22 a, a piezoelectric film 22 b, and a second electrode 22 c which are sequentially deposited so as to locate on the upper portion of the air gap 21.

The resonant part 22 is to filter a RF signal by use of a piezoelectric effect of the piezoelectric film 22 b. That is, the RF signal applied from the second electrode 22 c is output toward the first electrode 22 a through the resonant part 22. In this instance, since the resonant part 22 has a constant resonant frequency according to vibration generated by the piezoelectric film 22 b, only the signal which corresponds to the resonant frequency of the resonance part 22, among the input RF signals is output. In this embodiment, the resonant part 22 can be used to filter a signal suitable for the PCS using a GHz band.

The resonant part 22 is deposited on and supported by the piezoelectric substrate 10 in such a way that the first electrode 22 a covers a portion of the air gap 21. The piezoelectric film 22 b is deposited on and supported by the piezoelectric substrate 10 so as to cover the first electrode 22 a and the remaining upper surface of the air gap 21. The second electrode 22 c is deposited and supported to cover the upper portion of the piezoelectric film 22 b.

The first and second electrodes 22 a and 22 b are made of a common conductive substance such as metal. More specifically, the first and second electrodes 22 a and 22 b may be made of Al, W, Au, Pt, Ni, Ti, Cr, Pd, or Mo.

The piezoelectric film 22 b serves to cause a piezoelectric effect which converts an electric energy into a mechanical energy of an acoustic wave type, as described above. AN or ZnO may be used as a piezoelectric substance to form the piezoelectric film 22 b.

Each of the electrode pads 23 and 24 is deposited on the upper portions of the first and second electrodes 22 a and 22 c to have a specific thickness. The electrode pads 23 and 24 may be made of the same conductive substance as that of the first and second electrodes 22 a and 22 c. Reference numeral 25 in FIG. 1 denotes a support pad formed under the electrode pad 24 which is patterned and formed at the same time when the first electrode 22 a is formed.

The second filter includes an SAW device 30 having a good characteristic in the band of 900 MHz which is used for a cellular phone. The SAW device 30 includes an SAW device 31 and an SAW electrode pad 32 which are formed on the piezoelectric substrate 10.

The SAW device 31 can be formed in such a way that a comb-like electrode (InterDigital Transducer; IDT) surface faces up on the upper surface of the piezoelectric substrate 10. The SAW device 31 may be formed by depositing a metal substance on the piezoelectric substrate 10 in a desired pattern. In this embodiment, the SAW device 31 is made of the same substance as that of the first electrode 22 a, and is formed simultaneous with the first electrode 22 a. Therefore, the SAW device 31 may be made of Al, W, Au, Pt, Ni, Ti, Cr, Pd, or Mo.

The SAW electrode pad 32 is deposited on the upper surface of the piezoelectric substrate 10 in such a way that it is connected to the SAW device 31. The SAW electrode pad 32 is made of the same substance as that of the electrode pads 23 and 24 of the FBAR 20, and is formed simultaneous with the electrode pads 23 and 24. The multi-band filter module according to the embodiment of the present invention includes the construction in which the FBAR 20 and the SAW device 30 are concurrently formed on single piezoelectric substrate 10. Consequently, it can simplify the process of fabricating the multi-band filter module, and downsize and integrate the construction of the filter module.

The process of fabricating the multi-band filter module according to an embodiment of the present invention will now be described in detail.

A wafer level packaging method and a fabricating process of the multi-band filter module shown in FIG. 1 will now be described with reference to FIGS. 2A to 2F.

As shown in FIG. 2A, a sacrificial layer 11 for forming an air gap is formed on the upper portion of the piezoelectric substrate 10. After a groove is formed to have a specific depth at a point corresponding to the air gap 21 on the piezoelectric substrate 10, the groove is filled with a desired sacrificial substance to form the sacrificial layer 11. The groove for forming the air gap 21 may be formed by dry etching the upper surface of the piezoelectric substrate 10.

Next, as shown in FIG. 2B, after a desired metal substance is deposited on the piezoelectric substrate 10 and is patterned, the first electrode 22 a, the support pad 25, and the SAW device 31 are concurrently formed. The first electrode 22 a is formed to cover a portion of the sacrificial layer 11.

As shown in FIG. 2C, the piezoelectric film 22 b is deposited on the piezoelectric substrate 10 to cover the first electrode 22 a and the sacrificial layer 11.

Then, as shown in FIG. 2D, a desired metal substance is deposited on the upper portion of the piezoelectric film 22 b in a specific pattern to form the second electrode 22 c. The upper electrode 22 c may be made of the same substance as that of the first electrode 22 a or made of a substance different from that of the first electrode 22 a.

As shown in FIG. 2E, a desired conductive substance is deposited on the upper portion of the piezoelectric substrate 10 in a specific pattern to concurrently form the electrode pads 23 and 24 and the SAW electrode pad 32. Each of the electrode pads 23 and 24 is connected to each of the first and second electrodes 22 a and 22 c. The SAW electrode pad 32 is formed on the piezoelectric substrate 10 so that it is connected to the SAW device 31.

Next, the sacrificial layer 11 is removed, so that the air gap 21 is formed under the resonant part 22 with the first electrode 22 a, the piezoelectric film 22 b, and the second electric electrode 22 c deposited thereon. With the fabricating process, since the FBAR 20 and the SAW device 30 are concurrently formed on the same piezoelectric substrate 10, the fabricating process can be simplified, and filters having different bands can be downsized and integrated.

The multi-band filter module can be subjected to the wafer level packaging through a series of processes, as shown in FIG. 2F. That is, a multi-band filter module 100 fabricated by the above process is located under a packaging, as shown in FIG. 2F. More specifically, referring to FIG. 2F, the multi-band filter module 100 fabricated by the above method is provided under the packaging, and a wafer level packaging cap 200 is packaged and coupled to the upper portion of the filter module 100.

In FIG. 2F, reference numeral 41 and 42 denote a first sealing line provided on the electrode pad 23 and the SAW electrode pad 32, and reference numeral 43 and 44 denote a second sealing line provided on the packaging cap 200 corresponding to the first sealing lines 41 and 42.

The packaging cap 200 includes a cap wafer 210, a via electrode 220 penetrating through the cap wafer 210, and coupling pads 240 and 250 each provided on the upper and lower surfaces of the cap wafer 210. The coupling pads 240 and 250 are connected to the via electrode 220. The second sealing lines 43 and 44 are deposited and connected to the lower connecting pad 250.

By connecting the packaging cap 200 configured as described above with the upper portion of the filter module 100, the FBAR 20 and the SAW device 30 can be packaged as one package. Since the first and second sealing lines 41 and 42; 43 and 44 are made of a conductive substance, the filter module 100 is electrically connected to the coupling pad 240 provided on the upper portion of the cap wafer 210.

In the construction of the filter module configured as described above, a duplexer can be implemented by properly combining a plurality of the FBARs 20 or the SAW devices 30 in parallel or series.

The packaging cap 200 does not characterize the present invention. The construction of a prior packaging cap for the wafer level packaging can be coupled to the filter module 100 of the present invention to package the same.

Although not shown, the SAW device 30 and the FBAR 20 are packaged into one chip through the same wafer level packaging. In case a trimming circuit is required to improve characteristics of the SAW device and FBAR, a trimming circuit can be integrated on the piezoelectric substrate 10.

As described above, according to the present invention, the multi-band filter can be modularized by integrating the SAE device and the FBAR onto one substrate. Therefore, since some steps are partially concurrently performed in the process of fabricating the SAW device and the FBAR, the process can be simplified to reduce a manufacturing cost.

In addition, since the SAW device and the FBAR are unitarily packaged, the downsized and integrated filter module can be provided.

Additional connection is not required by directly fabricating the SAW and the FBAR on the piezoelectric substrate, thereby improving the signal loss characteristic the reliability.

While the invention has been shown and described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. 

1. A method of fabricating a multi-band filter module, the method comprising: (a) forming a Film Bulk Acoustic Resonator (FBAR) on a piezoelectric substrate; and (b) forming a Surface Acoustic Wave (SAW) device on the piezoelectric substrate; wherein the steps (a) and (b) are concurrently performed.
 2. The method of claim 1, wherein step (a) comprises: (a 1 ) forming a sacrificial layer, wherein the sacrificial layer is used to form an air gap to be recessed on a surface of the piezoelectric substrate; (a 2 ) sequentially depositing a first electrode, a piezoelectric plate, and a second electrode, on the piezoelectric substrate to form a resonant part; (a 3 ) depositing an electrode pad, which connects to the first and second electrodes; and (a 4 ) removing the sacrificial layer to form the air gap corresponding to the resonant part.
 3. The method of claim 2, wherein step (b) comprises: (b1) patterning the SAW device on the piezoelectric substrate; and (b 2 ) forming a SAW pad to be connected to the SAW device.
 4. The method of claim 3, wherein step (b1) is performed at the same time as when the first electrode is formed in the (a 2 ).
 5. The method of claim 4, wherein step (b 2 ) is performed concurrent with the step (a 3 ).
 6. he method of claim 3, wherein step (b 2 ) is performed concurrent with step (a 3 ). 